Alzheimer's disease is the most common dementia in aging humans, but its etiology is poorly understood. There is consensus that it relates in part to the toxicity and deposition of beta-amyloid fragments of the amyloid precursor protein. A key finding of beta-amyloid toxicity, even early in the clinical course of the disease, is oxidant stress. This manifests as lipid peroxidation and DNA damage in select cortical areas, followed by neuronal cell death. It follows that antioxidants, and particularly antioxidant vitamins such as ascorbic acid and alpha-tocopherol, should delay or prevent oxidant damage associated with beta-amyloid toxicity. However, this hypothesis has received little study. We propose to test it at the level of cultured neuronal cells and in animal models of Alzheimer's disease. Since neurons have the highest ascorbate content of any cell in the body, and since ascorbate is important as both a neuromodulator and antioxidant, we will focus on its role in preventing oxidant injury to cortical neurons. The first aim uses cultured SHSY5Y neurons to establish mechanisms of ascorbate uptake and recycling, to test whether ascorbate prevents lipid peroxidation and spares alpha-tocopherol, and to determine whether intracellular ascorbate either lessens beta-amyloid-induced oxidant stress or modifies beta-amyloid secretion. The second aim assesses the role of oxidant stress in the tissue damage and memory deficits in transgenic mice carrying mutations in key proteins implicated in human Alzheimer's disease. We expect to find that oxidant stress in these animals decreases cortical neuron concentrations of ascorbate, and that ascorbate supplements slow progression of cognitive defects by reversing local "scurvy." We will also crossbreed the transgenic mouse model of Alzheimer's disease with a knockout mouse that cannot synthesize ascorbate. If ascorbate prevents neuronal cell oxidant damage, moderate ascorbate deficiency due to dietary restriction should hasten the onset and worsen the severity of oxidant stress and cognitive deficits. In the third aim, we will use cortical neurons cultured from neonatal transgenic mice to determine at the cell level the mechanisms by which antioxidant vitamins lessen lipid peroxidative damage. If antioxidant vitamins ameliorate toxicity in cell and animal models of Alzheimer's disease, then oxidant stress is involved in disease progression, and antioxidant vitamin supplements may be beneficial.